1. Field of the Invention
The invention relates to a rotary tool having an engagement clutch torque of a motor to a tool bit and stops the torque transmission.
2. Description of the Related Art
As an example of a rotary tool having an engagement clutch, a known electric screwdriver for use in screw-tightening operation is disclosed in Japanese unexamined laid-open patent publication No. 2000-246657. In the known screwdriver, a driving-side clutch element driven by a motor is disposed opposite to a driven-side clutch element that rotates together with a spindle. In screw-tightening operation, when a driver bit is pressed against a workpiece, the driven-side clutch element is caused to move (retract) toward the driving-side clutch element together with the spindle so that the clutch teeth of the clutch elements engage with each other. As a result, the driver bit supported by the end of the spindle is drivingly rotated.
The known screwdriver is of the type in which the spindle rotates at high speed (for example, 6000 rpm). Therefore, a synchronizing mechanism is provided for rotating the driven-side clutch element in synchronizing with the driving-side clutch element. The synchronizing mechanism includes a biasing spring in the form of a compression coil spring that is disposed in a compressed state between the driving-side clutch element and the driven-side clutch element. The ends of the compression coil spring are slidably engaged with the driving-side clutch element and the driven-side clutch element via washers. In the state in which a screw-tightening operation is not being performed, the driven-side clutch element is pressed against a rubber stopper ring and held in a rotation prevented state. However, when the driver bit is pressed against the workpiece in order to start a screw-tightening operation, or when the driven-side clutch element moves toward the driving-side clutch element together with the spindle, the driven-side clutch element is disengaged from the stopper ring and thus released from the rotation prevented state. As a result, the driven-side clutch element synchronously rotates following rotation of the driving-side clutch element via the biasing spring. As a result, the clutch teeth of the driving-side clutch element and the driven-side clutch element can be smoothly engaged with each other.
In an engagement clutch having a synchronizing mechanism as described above, lubricant is applied to the sliding contact areas between the compression coil spring and the both clutch elements in order to reduce wear of the sliding contact areas. However, in the known construction, the compression coil spring is disposed on the inner peripheral side of the clutch elements and the grease flies outward by centrifugal force that is caused by high-speed rotation of the engagement clutch. As a result, a shortage of lubricant may possibly be caused on the sliding contact areas. Therefore, further improvement is required in the known engagement clutch with respect to the lubrication of the sliding areas.